1. Field of the Invention
The present invention relates to an electric machine tool having an electric motor for driving a rotating insertion tool, and to a method for controlling the electric machine tool.
2. Description of the Related Art
Electric machine tools such as drills or hammer drills are equipped with exchangeable insertion tools which are typically driven in a rotating manner by an electric motor of the machine tool. During operation of such a hand tool, the torque which occurs at the machine due to the rotation of the insertion tool is compensated for by a countertorque to be applied by the user. Depending on the operating situation, the torque load on the user may vary greatly. In particular, very high torque peaks may occur under unfavorable conditions. This is the case, for example, for a so-called kickback event in which the insertion tool becomes jammed in the workpiece. In particular for high-power machine tools, these torque peaks may represent hazardous working situations for the user. However, even for less high-power machine tools which are operated at a very high rotational speed, very large accelerations which last for several milliseconds may occur about the rotational axis of the electric tool due to the high level of rotational energy that is present in the system when the insertion tool suddenly becomes jammed.
To avoid the hazardous kickback situations, recent machine tools are equipped with appropriate protective functions which reduce the power of the drive motor when a sudden increase in torque occurs. Such a protective function is always activated according to the same criteria, regardless of the operating state or operating situation. Thus, for example, the kickback protective function is activated at a relatively low rotational speed when the insertion tool becomes jammed during operation of the machine tool, although the user himself would have sufficient time to release the machine tool switch being pressed by the user. On the other hand, in certain cases it is not possible to recognize, or correctly recognize, occurring kickback events based on the predefined evaluation criteria.